Generate separate anonymous class for each property reference

Each property reference obtained by the '::' operator now causes back-end to
generate an anonymous subclass of the corresponding KProperty class, with the
customized behavior. This fixes a number of issues:

- get/set/name of property references now works without kotlin-reflect.jar in
  the classpath
- get/set/name methods are now overridden with statically-generated property
  access instead of the default KPropertyImpl's behavior of using Java
  reflection, which should be a lot faster
- references to private/protected properties now work without the need to set
  'accessible' flag, because corresponding synthetic accessors are generated at
  compile-time near the target property

 #KT-6870 Fixed
 #KT-6873 Fixed
 #KT-7033 Fixed

compiler/testData/codegen/boxWithStdlib/reflection/properties/privateClassVar.kt

@@ -0,0 +1,31 @@
+import kotlin.reflect.IllegalPropertyAccessException
+import kotlin.reflect.KMutableProperty1
+import kotlin.reflect.jvm.accessible
+
+class A {
+    private var value = 0
+
+    fun ref() = A::class.properties.single() as KMutableProperty1<A, Int>
+}
+
+fun box(): String {
+    val a = A()
+    val p = a.ref()
+    try {
+        p.set(a, 1)
+        return "Fail: private property is accessible by default"
+    } catch(e: IllegalPropertyAccessException) { }
+
+    p.accessible = true
+
+    p.set(a, 2)
+    p.get(a)
+
+    p.accessible = false
+    try {
+        p.set(a, 3)
+        return "Fail: setAccessible(false) had no effect"
+    } catch(e: IllegalPropertyAccessException) { }
+
+    return "OK"
+}